The single biggest roadblock to the growth of commercial nuclear power in the United States is the resolution of the problem of nuclear waste storage or disposal. Until it can be demonstrated that nuclear waste can be stored safely, growth of the nuclear industry in this country will be seriously retarded. At the present time the general procedure for disposal of nuclear waste from commercial reactors, defense processes, and other sources is to first convert them into an alkaline solution. The liquid is then heated and evaporated to convert the waste into a powder called calcine. The calcine is mixed with borosilicate glass frit and is heated to melt the glass, either in the container in which it is to be stored or in a furnace from which it is poured into a storage container.
Due to corrosion problems with the glass produced by this process, an alternative process known as the cermet process, has also been developed. In the cermet process an iron nickel base metal matrix contains the fission product oxides from the high level waste. The cermet produced by this process is a continuous electrically conductive metal matrix containing small particles (about 1 micron) of waste oxide. The process is described more fully in U.S. Pat. No. 4,072,501. The final sintered waste cermet articles produced by this process could be in the form of pellets or rods. Currently cylindrical pellets 0.6 inches in diameter and 0.6 inches long are conveniently extruded.
Another process under consideration which avoids the high temperatures required in the borosilicate glass and cermet processes is to contain nuclear wastes in glass produced by the low temperature polymerization of metal alkoxides. These processes are described in U.S. Pat. application Ser. No. 162,967, filed June 25, 1980; U.S. Pat. application Ser. No. 176,738, filed Aug. 11, 1980; and U.S. Pat. application Ser. No. 162,966, filed June 25, 1980.
The product of all of these processes is a type of glass which contains the nuclear waste. The stability of the product depends on its ability to resist leaching or corrosive processes. Leach data for borosilicate glasses, for example, indicates that the glasses are not sufficiently resistant to leaching to provide long-term stability (i.e., greater than 500 years). Thus the alteration of these glasses is necessary before they can be safely used for the storage of nuclear waste.